Conventional greenhouse construction consists of an enclosure defined at least in part by materials such as glass or transparent plastics which will transmit the photosynthetic regions of solar radiation. The interior of the greenhouse is maintained at a suitable temperature by auxiliary heating systems to directly heat the air within the enclosure when the heating effect of the solar radiation is not adequate to maintain the minimum temperature requirements for the particular plants grown within the greenhouse.
The usual materials employed for greenhouse glazing, i.e., glass and relatively thin sheets of plastic, render the structure relatively energy inefficient, inasmuch as the losses during cold weather operation are extremely high due to the poor insulating characteristics of these materials and their relative thinness.
Such energy inefficiency has sharply curtailed the commercial employment of greenhouse farming techniques in cold climates and, with the steadily increasing cost of energy, has greatly reduced the use of greenhouse structures in raising food crops.
During many periods of operation of such greenhouses, the heating effect of the solar radiation exceeds greatly the heat required to maintain the temperature within the enclosure. This heat is normally rejected to the atmosphere by a ventilation arrangement, even during extreme low temperature conditions on bright, sunny days. In any commercial application, the cost of construction of the greenhouse is of course of paramount importance, representing capital investment. While more elaborate heat insulative materials could be utilized, as for example, thermal glass, this would greatly increase the construction costs.
In copending application Ser. No. 967,470, filed Dec. 7, 1978, there is disclosed a structural arrangement for improving the thermal efficiency by reducing the energy requirements of the greenhouse, utilizing a pivotal reflector-insulator member. This member consists of an insulating panel having a reflecting undersurface formed thereon, which panel is positioned in a raised position such as to admit solar radiation into the interior of the greenhouse during daylight conditions, the reflecting undersurface acting to reflect radiation into the interior to augment the direct sunlight. During nighttime or low light conditions, the panel is pivoted into a closed, covering position over the ceiling area of the greenhouse so as to provide insulation and retain the heat accumulated during the daytime.
Soil and gravel thermal storage media is employed absorbing and storing the solar energy which is rendered more feasible by the use of an insulated foundation structure.
During warm seasons, overheating and excessive illumination of the interior is the dominant problem often requiring shielding of the transparent panels forming the greenhouse structure.
It is therefore an object of the present invention to provide a greenhouse structure and method of growing plants under cold weather conditions in which the energy required is greatly reduced to improve the operating efficiency of the structure.
It is a further object of the present invention to more efficiently utilize the solar energy impinging on the structure for the purpose of maintaining minimum temperature variations within the interior of the greenhouse.
It is still a further object of the present invention to provide such high efficiency greenhouse structure with a construction which is relatively low in cost to fabricate such as to render the growing of plants commercially feasible in relatively severe northern climatic zones.